BAGHDAD — Iraq's pivotal national elections, originally scheduled for January, faced a likely delay of weeks or even longer after wrangling over a law setting terms for the polls broke down Monday.

Barring a last-minute reversal, a postponement will be at least a temporary setback for the Obama administration's hopes for Iraq, and perhaps even its plans for a swift drawdown of the 115,000 U.S. troops still in the country.

Secretary of State Hillary Clinton said in Washington that the election "might slip" as a result of the continuing dispute, but she expressed confidence that it will be held later.

Vice President Tareq al Hashemi, a Sunni Muslim, vetoed the law last week, complaining that it under-represented Iraqis living abroad, most of whom are thought to be Sunnis who fled after the toppling of dictator Saddam Hussein and the sectarian violence that followed.

On Monday, Kurds and Shiite Muslim politicians banded together and rebuffed Hashemi. They passed an amended version of the law with a formula that essentially would decrease Sunni voting power in several major provinces.

More than 50 parliament members walked out in protest, most of them Sunnis, but a smattering of secular lawmakers and Shiites joined them as well.

Many predicted that Hashemi would use his power as a member of Iraq's three-person Presidency Council and again veto the legislation.

"I believe that the amended law will be revoked by the vice president again and this will cause more delay and a higher possibility that there will be a constitutional void" and a government in limbo, said Osama al Nijaifi, a lawmaker from the secular Iraqia list.

A spokesman for Hashemi indicated the same outcome. "The matter is entirely in his hands, but he revoked it before because he felt there was injustice done to some of the Iraqis," Abdulilah Kathum told McClatchy. "This injustice is still in the amended law. In fact, it has become even more unjust."

Sunnis were outraged.

"I mourn to the Iraqi people today . . . the death of the constitution, and the death of justice," said lawmaker Ezz al Deen al Dawla.

The breakdown — after several recent moves and countermoves over the election law's constitutionality — underscores how sectarian politics still dominate Iraq, despite the security improvements of the past two years.

President Barack Obama is hoping to remove all U.S. combat forces from the country by August 2010. Under a U.S.-Iraq agreement, all troops must depart by the end of 2011.

Ideally, the White House wants to disengage and let Iraq repair and rebuild itself, but tensions remain high on several fronts.

Prime Minister Nouri al Maliki, a Shiite, has launched a campaign warning that forces loyal to Saddam are trying to regain power. On Sunday, his government put on television three suspects it said were behind Oct. 25 bombings, which killed more than 150 people in Baghdad; they said remnants of Saddam's Baath party were behind the attacks.

Others said that Maliki's charges of a Baath resurgence are overblown, and were aimed at scoring political points with his constituency.

"He thinks he will gain some votes from the street through this. . . . He may gain a bit of votes (from) the Shiites," Mahmoud Othman, an independent Kurdish legislator said in an interview. "But he is destroying his state. How could he build a state like this?"

Iraqi politicians, and especially Shiites who were severely repressed under Saddam, lack a "mentality of reconciliation," Othman said.

If Hashemi again vetoes the election law, it would take a three-fifths majority of parliament to override it.

Time is running short. The elections are supposed to be held by the end of January, but because of a major Shiite holiday, they can't be held in the last week of that month, and another multi-day holiday, when work stops, is approaching at the end this week.

Hashemi vetoed the election law because it gave 5 percent of the parliament seats to Iraqis living abroad. He wanted the share raised to 15 percent.

In response, the Kurdish and Shiite lawmakers agreed to give a share of votes from each province to the exiles. However, they added a poison pill: The elections would be conducted using 2005 voter rolls. Because of demographic changes and a Sunni boycott of 2005 elections, that would disadvantage provinces such as Ninevah, Diyala and Salahaddin, with large Sunni populations.

The original law was passed weeks late, after nearly a dozen delays over the disputed, oil-rich province of Kirkuk.

Nasreen Khalid Whab, a Kurdish member of Kirkuk's provincial council, said in an interview that political interference by Iraq's neighbors was making the situation even more difficult.

"It's impossible to be satisfied 100 percent," she said of the election law. "There's no such thing."

(Issa is a special McClatchy correspondent. Strobel reported from Kirkuk, Iraq. McClatchy special correspondent Mohammed al Dulaimy contributed to this article.)